1. Field of the Invention
This invention relates to the manufacture of semiconductor devices, and in particular, to a method of and device for preventing short circuits between solder joints in flip chip packaging.
2. Description of Related Art
Multi-layer ceramic electronic components are typically joined together by soldering pads on a surface of one of the electronic components to corresponding pads on the surface of the other component. Controlled Collapse Chip Connection is an interconnect technology developed by IBM as an alternative to wire bonding. This technology is generally known as C4 technology or flip chip packaging. Broadly stated, one or more integrated circuit chips are mounted above a single or multi-layer ceramic substrate and pads on the chip are electrically and mechanically connected to corresponding pads on the substrate by a plurality of electrical connections such as solder bumps. The integrated circuit chips may be assembled in an array such as a 10×10 array on the multi-layer ceramic surface.
Often in flip chip packaging, a semiconductor chip is joined to a substrate by means of solder joints where an array of connections from the chip are connected to a corresponding array of connections on the substrate using solder such as a lead/tin alloy. The solder is deposited on bonding pads located on the surface of the chip and substrate by means of evaporation or plating and then reflowed to cause the solder to wet the I/O pad. The chip is placed on the substrate and fluxed to ensure good wetting between the I/O pads and the solder. The chip and substrate are then subjected to a higher temperature causing the solder to melt and wet each I/O pad on the package. The assembly is cooled causing the solder to solidify, thereby providing one or more electrical connections between the chip and the substrate forming an electronic package.
Subsequently, the assembly can be cleaned to receive a nonconductive underfill to reduce the fatigue of the solder joints between the chip and the substrate. In underfiliing the electronic package to provide additional stability of the solder joints, a polymer with ceramic or glass filler is allowed to flow under the chip, between the solder connections, and later heated at an elevated temperature causing the polymer or filled polymer to cure. In this structure and method, added cost in production is incurred due to the sequential operations of solder depositions, reflow, join, reflow, underfill, and polymer cure.
The prior art methods of flip chip assembly do not prevent the solder joints from being over compressed when the chip and substrate are joined. Deformity of the solder joint can lead to short circuits when one solder joint is in contact with an adjacent solder joint. Underfilling will not prevent the shorting since the solder-to-solder contact has already been made. Thus, it is desirable to have a means of preventing short circuits between adjacent solder joints which would result in increased yield and reliability of the resulting electronic module.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide a method of preventing short circuits between solder joints in an electronic module.
It is another object of the present invention to provide an apparatus and method of fabricating the apparatus for preventing short circuits between solder joints in an electronic module.
A further object of the invention is to provide a method of assembling an electronic module having enhanced yield and reliability.
It is yet another object of the present invention to provide an electronic module having enhanced reliability.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.